The invention relates to a process for separating hydrogen from a gas flow having an oxygen constituent comprised predominantly of hydrogen, nitrogen, oxygen, carbon dioxide, carbon monoxide, methane and/or other hydrocarbons as well as a device for conducting the process.
The invention is described using the example of separating hydrogen from coke oven gas, but is suitable for separating hydrogen from any gas flow of any composition of the above-mentioned components and is therefore not limited to coke oven gas.
When coke is manufactured in coking plants, for the most part bituminous coal is heated with the exclusion of air. Coke, coke oven gas and tar are generated in the process. The more carbonaceous coke is used mainly in the production of iron. The coke oven gas comprised predominantly of hydrogen, methane and carbon monoxide is used mainly as an industrial fuel according to the prior art. However, coke oven gas has only about half the heating value of natural gas and is frequently contaminated by accompanying substances, which can cause the emission of toxic substances or operating malfunctions. As a result, because of stricter environmental guidelines, efforts are being made to find alternative uses for coke oven gas.
Coke oven gas is often comprised of approx. 60% hydrogen. Among other things, hydrogen is required in large quantities in oil refineries to reduce the sulfur content of middle distillates in what is commonly known as hydrotreaters and to break down different crude oil fractions in so-called hydrocrackers. In addition, hydrogen is used in the reduction of metal oxides, the manufacturing of ammonia, as a propellant, or in fuel cells. European Patent Document No. EP 1033346 describes a prior art process for separating hydrogen from a gas flow, which, in addition to hydrogen, contains predominantly nitrogen, carbon dioxide, carbon monoxide and methane along with the impurities of oxygen and argon.
In the case of a process for pressure swing adsorption according to the prior art, the gas mixture is fed under high pressure to a reactor having an adsorber. Depending upon the prevailing pressure and the adsorber material, the components of the gas mixture are adsorbed by the adsorber material at different intensities. In an ideal case, all components of the gas mixture are adsorbed by the adsorber with the exception of hydrogen. Hydrogen is thus separated from the remaining components with a high level of purity. Regeneration of the adsorber takes place at low pressure by desorption of the bound components, which can then also be withdrawn in a gaseous manner from the reactor. Thus, hydrogen having a high level of purity can be separated from the remaining gaseous components using a pressure swing adsorption process by using several reactors, which adsorb and/or desorb in an alternating manner. By using the process described in EP 1033346, hydrogen with a purity of a maximum of 99.99% can be separated from the remaining gaseous components.
An increased safety risk arises when using this type of process according to the prior art in the case of oxygen constituents in the gas flow of greater than 1% by volume. The oxygen present in the gas mixture is adsorbed to begin with at high pressure in the adsorber, but in the subsequent course of things is again displaced into the gas phase by components that are being adsorbed more powerfully. This produces oxygen enrichment in the adsorber so that an ignitable, explosive mixture is produced in combination with the hydrogen present in the gas. This explosive mixture represents a safety risk in a pressure swing adsorption process according to the prior art.
The present invention is therefore based on the objective of devising a process of the type mentioned at the outset that avoids the formation of an explosive hydrogen-oxygen gas mixture and minimizes the safety risk of this type of process.